A popular system for providing e-mail messages to mobile wireless communication devices is a push e-mail system. That is, a system where a Mail Delivery Agent (MDA) sends (or pushes) newly received e-mail messages to a Mail User Agent (MUA). An MUA (or e-mail client) is a computer program that is used to read, compose and send e-mail messages.
Historically, the MDA is software that accepts incoming e-mail messages and distributes each e-mail message to a mailbox of the recipient. Such distribution was particularly straightforward when the mailboxes resided on the same computing device that executed the MDA software. The distribution became more complex as the mailboxes were distributed to storage on other computing devices networked to the computing device that executed the MDA software. More recently, complexity of distribution increased as recipient mailboxes, and MUA software, were placed on mobile wireless communication devices. A popular push e-mail system for mobile devices uses wireless MUA devices and a push e-mail server attached to a traditional e-mail system. The push e-mail server monitors the e-mail server and, when the push e-mail server identifies a new e-mail message for a user of a wireless MUA device, the push e-mail server retrieves a copy of the new e-mail message and pushes the new e-mail message to the wireless MUA device over the wireless network.
Competition for the push system for providing e-mail messages to mobile wireless communication devices is provided by a pull e-mail system. In a pull e-mail system, the MUA polls the MDA at intervals to determine whether there are new e-mail messages and, if so, downloads the new e-mail messages. The known Post Office Protocol version 3 (POP3) is a popular example of a pull-based mail delivery protocol. In contrast to pull e-mail, most of the protocols used in popular current systems of push e-mail are proprietary.
While pull e-mail may have initially been considered better suited to wireless e-mail message delivery, due to wireless data devices not always being available to receive e-mail, certain aspects of push e-mail systems has made push e-mail systems very popular. For instance, where users of wireless data service networks are charged by the kilobit, each time the wireless data device polled the pull e-mail server, the charges to the user would increase. Additionally, polling the server when no e-mail messages are present may be seen as wasting the energy stored in the battery of the wireless data device. However, it appears that the instantaneous nature of e-mail message delivery in push e-mail systems has been the primary factor in increasing the popularity of push e-mail systems.
Efforts to reduce, in a pull e-mail system, the delay between the arrival of an e-mail message at the e-mail server and the arrival of the e-mail message at the wireless device, minimization of which delay is a feature of push e-mail systems, have largely centered around reducing the polling interval. That is, increasing the frequency with which the wireless MUA device polls the MDA to see if there are new e-mail messages. However, as discussed above, an increased frequency of polling is known to detrimentally result in an increase in network traffic that is costly to the user and wasteful of battery life.